1. Field of the Invention
The present invention relates to an ignition device for an internal combustion engine, and more particularly to a method and device for controlling the ignition timing of a capacitive discharge ignition device.
2. Description of the Related Art
A strong demand exists for providing an accurately controlled ignition timing at a desired point in time to provide safe and efficient operations, reduced fuel consumption, and clean exhaust gases for an internal combustion engine. To this end, as disclosed in Japanese Published Examined Patent Application No. H-7-26602, the ignition timing is controlled using a microcomputer.
The aforementioned conventional technique is designed to provide a power supply circuit for converting an output voltage from a generator coil (exciter coil) into a direct voltage so as to employ the power supply circuit as a power supply for the microcomputer. During a low speed operation of the engine, the technique provides an ignition signal using a low-speed ignition position signal supplied by a pulser coil, and measures the ignition position, calculated in accordance with a pulser coil external interruption signal, by counting clock pulses to perform ignition operations.
This design provides advantageous functions that make it possible to operate the microcomputer without a battery and perform an ignition operation even during at a low speed operation, including the time of start-up, of an engine which cannot provide a voltage available to the operation of the microcomputer.
Some capacitive discharge ignition devices for an internal combustion engine employ a method for preventing over-rotation of an ignition device having no pulser coil for generating a signal to define an ignition timing, in which an over-rotation of RPM of an internal combustion engine causes an ignition operation of the ignition device to be stopped, i.e., to be in a misfire state (e.g., Japanese Published Unexamined Patent Application No. H-11-173248).
The technique disclosed in Japanese Published Unexamined Patent Application No. H-11-173248 detects the RPM of an internal combustion engine in accordance with the magnitude of a forward voltage portion of an output voltage from a generator coil (exciter coil) in a capacitive discharge ignition device. The technique defines, as a steady-state control mode, the detected RPM being at an operation upper limit speed or less, i.e., the upper limit of the range of operation speeds which is preset and regarded as being appropriate to operate a load, and defining the detected RPM being above the operation upper limit speed as an over-rotation prevention control mode.
In the steady-state control mode, a rechargeable capacitor is recharged each time the generator coil generates a forward voltage portion of the output voltage to perform a proper ignition in the internal combustion engine.
In the over-rotation prevention control mode, misfire control and ignition recovery control are alternately provided to recover the control mode to the steady-state control mode when the RPM detected during an ignition period is at the operation upper limit speed or less. The misfire control short-circuits the forward voltage portion from the generator coil to stop ignition operations during a preset misfire period, whereas during a preset ignition period, the ignition recovery control releases the short-circuiting of the forward voltage portion from the generator coil to recover the ignition operation provided by the ignition device and detects an RPM in accordance with the magnitude of the forward voltage portion from the generator coil.
This design provides an advantage of detecting the RPM of the internal combustion engine with stability in accordance with the forward voltage portion from the generator coil which is not affected by the armature reaction during an ignition period, thereby making it possible to provide control for maintaining the RPM at the operation upper limit speed or less. The design also provides an advantage of eliminating the need to provide a special sensor for detecting the RPM of an internal combustion engine, thereby simplifying the structure thereof.
On the other hand, some known stop means for an ignition device for an internal combustion engine connect a stop switch in parallel to a generator coil to manually turn on the stop switch, thereby short-circuiting between both terminals of the generator coil to disable the ignition operation and thus stop the operation of the internal combustion engine.
This stop means employing only the manual stop switch has a disadvantage in that although a stop switch formed of a push-button self-recovery normally open contact switch provides an easy stop operation, it requires continuously pressing the stop switch until the internal combustion engine comes to a complete stop, thus complicating its handling.
Additionally, the stop switch formed of a sliding self-hold switch provides an advantage of self-holding an ON state with stability, thus making it possible to reliably stop the internal combustion engine by switching the stop switch to the ON state. On the other hand, such a disadvantage is also provided where the internal combustion engine may be started without having switched the stop switch to an OFF state, thereby making it difficult to re-start the internal combustion engine.
In this context, a conventional technique available to solve these disadvantages provides means configured such that both ends of a generator coil are connected with a series circuit that includes a self-recovery stop switch and a rechargeable/dischargeable capacitor, and with the anode and cathode of a switching element, with the gate of the switching element being connected to a discharge circuit of the rechargeable/dischargeable capacitor (e.g., see Japanese Published Unexamined Patent Application No. 2000-240549).
However, the aforementioned prior art disclosed in Japanese Published Examined Patent Application No. H-7-26602 requires a pulser coil external to the generator coil, thereby raising a problem of the generator being made complicated in structure, and requiring high dimensional accuracy during assembly leading to complicated handling.
There was also another problem in that an ignition operation is performed even at the time of a low speed operation of an engine which cannot provide a voltage available to the operation of the microcomputer, causing the engine to operate very unstably at a low speed and especially to operate unstably at the time of a start-up.
There was still another problem in that the low-speed ignition position signal supplied by the pulser coil is always generated at constant rotational angle intervals because the pulser coil is fixed immovably, thereby making it impossible to provide an advancing operation suitable for the speed of the engine in the low speed region and thus eliminate the instability in low speed operation of the engine.
Furthermore, even when a microcomputer controls the ignition timing in the low speed region of the engine, the ignition timing is set by counting clock pulses of a temporal signal, which is set in accordance with the information on the RPM obtained, from a constant starting position of counting. Thus, there was another problem in that occurrence of variations in rotation typical of the low speed region, causing the RPM of the engine to be reduced at the time when the piston approaches the top dead center, would result in a significant advance in ignition timing, thereby leading to the possibility of a kickback occurrence.
In the aforementioned prior art according to Japanese Published Unexamined Patent Application No. H-11-173248, the over-rotation prevention control mode is made up of the misfire control and the ignition recovery control to alternately provide the misfire control and the ignition recovery control. However, since the ignition recovery control is completely the same as the ignition control in the steady-state control mode, the RPM of the internal combustion engine that has started to decrease due to the misfire control is raised again by the ignition recovery control. Thus, there was another problem in that it proves difficult to smoothly reduce the RPM of the internal combustion engine.
To eliminate the occurrence of the aforementioned drawbacks, it is also conceivable to provide the misfire control with a time width sufficient for the RPM to reliably reduce below the operation upper limit speed. However, this eliminates the need for the ignition recovery control in the over-rotation prevention control mode, providing no meaning to the aforementioned prior art. In this case, there is a problem in that the difference between the RPM in the misfire state and the RPM at the time of the ignition state being restored is likely to become bigger, thereby causing a load to be operated under significant variations in speed and lack of smoothness.
It is certain that the aforementioned prior art disclosed in Japanese Published Unexamined Patent Application No. 2000-240549 allows the internal combustion engine to be reliably stopped by a simple depression of a push-button switch or the stop switch. However, the ignition control circuit serving as a main portion of the ignition device requires proper setting of a circuit constant such as impedance, complicated handling such as setting of ratings of each of the parts constituting the stop means, and complicated connections to the ignition control circuit. This raised a problem of requiring time and effort for handling and implementation.
There was also a problem in that occurrence of a failure such as a short-circuited or open rechargeable/dischargeable capacitor or switching element leads to a loss of a stop function thus providing no fail-safe function.
Furthermore, to stop the internal combustion engine, the technique also requires, as dedicated parts in addition to the stop switch, the rechargeable/dischargeable capacitor and the switching element as well as a backflow blocking diode and resistive element. Thus, this raised a problem in that forming the stop means requires a number of parts, thereby making its structure complicated as well as raising its costs.
In the aforementioned prior art according to Japanese Published Examined Patent Application No. H-7-26602, the rising edge of a recharge voltage, at the time of start-up of the internal combustion engine, in a constant voltage power supply portion for recharging the reverse voltage portion of the generator coil is delayed due to the current limiting resistor provided for security of the input portion, thereby making it impossible to start up the microcomputer quickly. Thus, there was another problem in that since a recoil starter had to be used to rotate the internal combustion engine at least three to four times to provide ignition, its start-up characteristics were not always good.
In this context, the present invention was developed to solve the aforementioned prior art problems. It is therefore an object to technically simplify the structure of a generator and stabilize the operation of an engine at the time of start-up, thereby providing an ignition device simplified in structure and reduced in size and providing improved safety to the engine.
It is another object to technically stabilize the operation of the engine in the low speed region including at the time of start-up, thereby providing improved safety to the engine and secure ignition operations.
It is still another object with an ignition device for a capacitive discharge internal combustion engine to technically maintain the RPM of the internal combustion engine reliably with stability at the operation upper limit speed or less which is a preset upper limit of the operation speed region in which a load can be operated efficiently with stability, thereby providing improved safety to the engine and providing efficient operations to the internal combustion engine.
It is still another object to technically ensure the internal combustion engine to be safely stopped in a simple and reliable manner, thereby providing simplified handling and structure, realizing a high fail-safe level, and allowing manufacturing and implementation at low costs.
It is still another object to technically allow the microcomputer to start up quickly at the time of start-up, thereby providing improved start-up performance to the engine.